What behavior signals if a woman or man is interested in someone?

The number one tip-off that a woman was interested in a man for more than friendship was her own speaking rate. Did she talk smoothly and quickly (a good sign), or hesitantly and awkwardly?

And:

The technology developed by Sandy Pentland and his colleagues at MIT Media Lab counts the number of times people say “uh-huh,” “yeah,” “yup,” “aha,” “okay,” and “I see” when they’re listening to someone speak. In Pentland’s study, the more short interjections a man made, the more attractive he was to the woman who was talking.

And:

Men’s romantic interest was predicted most by how much the woman spoke. They were also reportedly more interested in women who varied their tone (up-and-down frequencies).

And as an overall predictor:

The more engaged the woman was in the conversation, the better the outcome.